Capacitive Position Sensor Bezel-less Design
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Solution Overview
Problem
Existing two-dimensional touch-sensitive position sensors require a bezel opening for direct user contact, leading to moisture and dirt ingress issues, are expensive to produce, and have complex sensing circuitry, while discrete capacitive keys offer limited resolution and cannot be produced on a mass scale without a bezel.
Innovation Solution
A capacitive position sensor with a single layer of electrodes arranged in a matrix of columns and rows, where electrodes are electrically coupled within the sensing area and externally, allowing for a bezel-less design, reduced manufacturing costs, and improved resolution through fewer measurement channels and interleaved electrode patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a bezel opening is provided for direct user contact with the sensing layer, then touch sensitivity and resolution are improved, but sealing against moisture and dirt becomes difficult and manufacturing cost increases
Solution Approach 1:
The sensing layer is inverted from the traditional front-surface location to the rear surface of the panel. This allows the sensing elements to be positioned on the back side, eliminating the need for front surface openings while maintaining capacitive coupling through the panel thickness. The wrap-around connections extend the sensing area to the edges, enabling full-surface coverage without bezel openings.
Solution Approach 2:
The sensing approach transitions from a two-dimensional surface contact model to a three-dimensional volumetric coupling model. The capacitive sensing extends through the thickness of the panel, allowing electric field penetration from the rear surface to detect touches on the front surface without requiring direct access to the sensing layer.
2Measurement precision
If a matrix of conductors is used for continuous XY position sensing, then resolution is improved, but the number of sensing layers and circuit complexity increase
Solution Approach 1:
The sensing area is segmented into discrete sensing cells arranged in a grid pattern, with each cell defined by intersections of row and column electrodes. This segmentation allows the use of fewer measurement channels while maintaining continuous position resolution through signal processing and centroid calculation from the activated cells.
Solution Approach 2:
Multiple row and column electrodes are electrically combined through wrap-around connections that extend the conductors around the edges of the sensing area. This merging approach allows a reduced number of measurement channels to monitor multiple electrode intersections, decreasing circuit complexity while preserving sensing coverage.
3Ease of manufacture
If discrete electrodes are used for capacitive sensing, then manufacturing cost is reduced, but position resolution is limited
Solution Approach 1:
The physical parameters of the electrodes are optimized to enhance capacitive coupling efficiency. The wrap-around connections increase the effective sensing area and improve electric field distribution, allowing discrete electrodes to achieve higher resolution than traditional discrete key designs while maintaining manufacturing simplicity.
Solution Approach 2:
The mechanical contact requirements of traditional discrete keys are replaced with capacitive coupling through the panel thickness. This substitution eliminates the need for physical switches or membrane contacts, allowing simpler discrete electrode structures to achieve continuous position sensing through electrical field interactions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables a cost-effective, bezel-less touch surface with improved resolution and durability, suitable for various devices, including portable electronics and kitchen appliances, by using a single layer of electrodes and efficient capacitance measurement channels.
Implementation Method 1
capacitive position sensor for determining the position of an object within a two-dimensional sensing area
Data Source
AI summary
A capacitive position sensor for determining the position of an object along first and second directions is described. The sensor comprises a substrate having an arrangement of electrodes mounted on a single surface thereof. The electrodes are arranged so as to define an array of sensing cells arranged in columns and rows to form a sensing area. Each of the sensing cell including a column sensing electrode and a row sensing electrode with the column sensing electrodes of sensing cells in the same column being electrically coupled together and the row sensing electrodes of sensing cells in the same row also being electrically coupled together. Row sensing electrodes of sensing cells at opposing ends of at least one of the rows are connected together by an electrical connection made outside of the sensing area so that there is no requirement for electrical connections to cross within the sensing area, thus providing a capacitive position sensor having a sensing area with electrodes on only one side of a substrate.